So I've learned that a common noob pitfall is playing too many cards from your hand and falling behind on cycling your deck, where 'too many' is generally 2 or more.

Given that, when should one play Charge from the red starter deck? (+1 ATK and HASTE to a unit) For haste to be useful I probably needed to play something this turn from my hand. How valuable of an objective would it need to be to be worth playing this extra card from my hand? Or should I think of it as a card that gives +1 ATK in the early game, and don't think about the haste until the late game when it might be worth the tempo boost to attack a turn early?

1: Red is generally an aggressive color in general, so you can fall behind in cards if you're accruing another advantage (such as tempo: getting ahead in board)2: Going down to 4 cards on one turn will slow your cycling, but it won't necessarily significantly slow it, and you can always use the Technician slot in your Patrol Zone to recoup the deficit. Pay attention to how many cards are in your deck/discard; the "lost" card might not even be relevant, if you've played so many cards that your discard is very slim.

As a general rule, yes, you want to refill your hand to 5 each turn (although I have been up against a rush down player who just skipped playing a worker for several turns and was able to play 2-3 cards each turn that way).

I personally like it as an ambush card. I'm not really a rush down player myself, but for example, paired with fire spec, you have a lot of ways to eliminate a blocker, then drop a card and play this on it mid-late game where only drawing 4 cards isn't a problem. A surprise hasted land octopus earl-mid game is not going to be happy fun times for your opponent.

You probably want to play Charge if that takes out a tech building or a hero who is obviously going to cast a devastating (ultimate) spell. Sometimes taking out a tech building can incapacitate enemy production for two turns, (e.g. when they currently have 7 or 9 workers), which is like forever in this game if one is being battered by a significant board.

Charge is only a unit; Geiger's Now! from the Present line says "unit or hero".

And yeah, you are pretty much committing to not making a worker or going down on cards when you play Charge. For Red, this can be totally okay sometimes. It can be tough for Red to make use of the Technician slot, but cheap blockers like Crash Bomber fit there beautifully.

Don't forget that if midband Zane kills an enemy Technician, you'll draw a card. This can help you gain the tempo to cast Charge and keep on crushing.